The present invention relates to a method of assembling a tire carcass and the tire resulting therefrom.
The conventional pneumatic tire comprises a toroidally-shaped tire carcass which extends between two wheelrim-engaging bead regions through sidewall regions and a ground contacting tread region. The carcass is reinforced by one or more plies of rubber fabric having axially extending reinforcements which pass through the tread and sidewall regions and are anchored in their edge portions to an annular inextensible bead core in the radially inner part of the bead region
One of the problems facing the tiremaker is ensuring that the ply edge remains in the correct position in the bead region during assembly of the remainder of the tire components whilst accommodating intermediate and/or final shaping of the resultant uncured tire blank prior to vulcanization.
One solution to the above problem which has been widely adopted is to turn the ply edge portion fully around the annular bead core before shaping the ply into a toroid.
Such a construction however is both wasteful of carcass ply material forming the turnup and has the further disadvantage that the ply ending is taken into the region of greater flexure which tends to increase the risk of ply edge looseness problems during later service life of the tire.
Another proposal applicable particularly where the carcass reinforcement comprises one or more cords wound continuously in a zigzag configuration from bead to bead is to hold each ply end loop as it is formed on a small hook or pin so that the whole periphery of the ply edge is temporarily secured in position during assembly of the uncured tire. However the additional equipment necessary to implement this on the tire building machine is complex and expensive and tire production is slow.
It is an object of the present invention to provide a method of assembling a reinforcing ply in a tire carcass and a tire carcass construction which avoids the above-mentioned problems.
According to one aspect of the present invention a method of assembling a tire carcass comprises applying a cord reinforced rubber ply to a toroidal-shaped former such that the edges of the ply are located on radially inner portions of the former, placing a circular bead component adjacent to each edge and stitching each ply edge to its said circular bead component to secure the ply edge in the region of the tire bead without forming a turn-up. A cured tire is formed by subsequently assembling tire components and the tire carcass to form a tire and curing the tire.
The stitching step may comprise sewing the cord ends of the ply to the circular bead component. Alternatively the stitching may comprise pushing needles through the cord ends and in to the circular bead component so as to press and engage the cord ends in the circular bead component.
The circular bead component may be a conventional bead or an additional component and in that case the stitching step comprises stitching the cord ends in to the bead hoop or separately the component member.
A second aspect of the invention provides a tire carcass comprising two spaced-apart bead regions, two sidewalls, a central tread region and a toroidal reinforcement ply comprising a rubber sheet reinforced by reinforcement cords wherein the component ply has in each bead region a ply edge which is located in its bead region by being stitched to a circular bead component adjacent to said edge.
The circular bead component may be an additional bead component or an inextensible bead hoop which may comprise a winding of steel wire, aramid or a ring of plastics material.
Where the circular bead component is a separate component it may comprise a precured rubber ring or preferably a ribbon or tape of fabric to hold the reinforcement ply edges during subsequent tire assembly. The fabric rubber or tape may be conventional tire fabric or may be of elastic cords to allow a degree of stretch.
The stitching of the reinforcement cords to the circular bead component may be by means of a thread or filament which passes in to the circular bead component at spaced-apart intervals between which it passes over successive cord ends. Alternatively the cord ends themselves may be engaged in the circular bead reinforcement by needling. The invention is particularly advantageous with a tire comprising a single cord reinforcement for the carcass ply wherein the cord is looped in each bead region so that it goes back parallel to itself from bead to bead.